1. Field of Invention
The invention relates to the technique of manufacturing floating bodies made of synthetic resins reinforced by continuous fibers and produced on a winding apparatus.
2. Description of Related Art
Floating bodies made of synthetic resins reinforced by fibers are conventionally manufactured by contact molding, of resin-impregnated chopped fibers, on female molds or master patterns in several parts. The cutting, laying-down and impregnating phases, excluding the case of pre-impregnated fibers, are generally carried out manually. The fibers are in the form of unidirectional, two-directional or three-directional fabrics or in the form of randomly oriented short fibers.
This process has the drawback of contacting noncontinuous and nonstressed reinforcing fibers, hence unpredictable mechanical properties, and a resin applied manually, hence in general an irregular resin content. These two characteristics result in an unnecessary increase in the weight.
This process is only partly automatable. Because of the necessarily manual work, the manufacturing times cannot be improved.
This long manufacturing time does not allow a large complex part to be manufactured easily, such as the deck and the hull of a yacht, which are rarely solidified in just one go and at the same time; thus, the mechanical properties of the end product are limited because of the joining operations carried out after solidification which weaken the structure, for example the deck-hull junction on a boat. In addition, these joining operations increase the risks of the composite delaminating or debonding at the junction points, with the presence of edges at the bonded joints on the various parts joined together, risks which are not negligible in water.
In addition, contact impregnation of the fibers does not allow certain resins having high properties, and harmful via the airways or on contact with the skin, to be used.
There is a processxe2x80x94filament windingxe2x80x94which consists in winding, over a mandrel having the shape of the part desired, resin-impregnated continuous fibers placed in predetermined directions. Using this filament winding process, the continuous fibers are wound, on the one hand, homogeneously in the direction of the main stresses and, on the other hand, locally in the highly stressed regions.
This technique has the drawback of not being able to guarantee the external surface finish of the wound parts and of requiring, for some applications, finishing treatments, the use of a countermold before solidification or a machining operation after solidification. In this field, we mention document U.S. Pat. No. 3,265,795 which describes xe2x80x9ca method of molding a fiber-reinforced plastic shellxe2x80x9d. This process, which uses an inflatable mandrel and a countermold, provides one solution to the problem of the external surface finish but does not describe the manufacture of products having a nondevelopable surface. Another solution is given in document U.S. Pat. No. 4,849,150 A which describes xe2x80x9ca method of manufacturing a pipe made of fiber-reinforced resinxe2x80x9d. This method consists in injecting resin into a countermold, but is described only for pipes, and requires the use of specific materials.
Another drawback of the filament winding relates to the winding of structures having decreasing cross sections, a common case in floating craft. The difficulty is to maintain the fiber orientations and the thicknesses defined for the mechanical strength of the structure. Firstly, in decreasing cross sections, the fibers can slide over the mandrel and the additional thicknesses obtained in the small cross sections do not correspond to the desired thicknesses. Secondly, the structure obtained is not symmetrical with respect to the plane of symmetry of the mandrel. On this subject, document FR 1,590,718 A describes a xe2x80x9cprocess for manufacturing a structure of any shape, the machine for implementing said process and the structures produced by said processxe2x80x9d. This process makes it possible to lay down tapes on a body with decreasing cross sections but does not describe either the use of a fiber-reinforced thermosetting plastic or a lay-up other than radial lay-up. In this field, we also mention document U.S. Pat. No. 3,300,355 A which describes xe2x80x9ca method of manufacturing hollow bodies of irregular shapexe2x80x9d. This method makes it possible to lay down tapes on a body, with decreasing cross sections and groovings for producing reinforcements, but does not describe either the use of fiber-reinforced thermosetting plastic or a lay-up other than radial lay-up. Document U.S. Pat. No. 4,849,150 A, which describes xe2x80x9ca method of manufacturing fiber-reinforced resin pipexe2x80x9d, already mentioned, does not describe a specific winding method allowing a symmetrical structure without an overthickness to be obtained.
Another drawback of the filament winding process is the manufacture and the recovery of the mandrel after the winding. Document U.S. Pat. No. 4,494,910 A, which describes the manufacture of xe2x80x9cstructural components having a large surface area; especially rotor bladesxe2x80x9d, presents a technique in which the mandrel is kept in the final part, but does not describe the manufacture of hollow parts. Document EP 0,216,695 A describes xe2x80x9ca process and a machine for the manufacture of axisymmetric hollow parts formed from filaments extending along three different directionsxe2x80x9d. This process presents a solution in which the mandrel is machined on the winding apparatus, but it is described only for axisymmetric hollow parts. Document U.S. Pat. No. 3,265,795, already mentioned, which describes xe2x80x9ca method of molding a fiber-reinforced plastic shellxe2x80x9d, presents a method for recovering the mandrel, using two parts together, but does not describe a method for manufacturing a single part.
The invention can provide a solution to the drawbacks currently encountered in the manufacture of floating bodies made of synthetic composites, by producing them with continuous fibers on a winding apparatus, after having solved the problems posed by this manufacturing process currently unsuitable for producing such products.
The invention relates especially to a process for manufacturing a floating body, such as a boat""s hull or part of such a hull, defined in the claims and which includes at least one filament winding step. This process comprises, depending on the embodiments, the combination of steps providing for:
producing a first mandrel in the form of a preform, having substantially the external shape of the floating body to be manufactured;
mounting this first mandrel on a winding apparatus and, optionally, subjecting it to a treatment of refining its external shape;
covering this first mandrel, at least partly, by winding or filament winding resin-impregnated fibers so as to obtain an outer mold or countermold, whose internal surface will undergo a treatment, such as coating with a mold release and/or with a topcoat forming the external surface of the floating body to be manufactured;
after solidification, cutting the countermold into at least two demoldable portions, for example along a longitudinal plane of symmetry;
producing a second mandrel in the form of a preform, having substantially the internal shape of the floating body to be manufactured;
mounting this second mandrel on a winding apparatus and, optionally, subjecting it to a treatment of refining its external shape;
covering the second mandrel, at least partly, by winding or filament winding, with or without resin impregnation, in order to obtain a wound body which will be the floating body;
putting the materials of the floating body between the second mandrel and the countermold under pressure;
after solidifying the materials of the floating body, such as curing, disengaging the countermold and/or subjecting the floating body to a refining treatment, cutting out at least one reservation in the latter, for example for the passage or the joining of items of equipment such as masts, keel, deck house or the like and/or for removing at least one portion of the mandrel.
A second subject of the invention is a formation of the mandrels intended for implementing the process according to the claims. A third subject of the invention is the apparatus for implementing the process according to the claims.
According to the characteristics of the invention:
The treatments of refining the external surfaces of the mandrels entail the fitting of winding-assistance devices, of suitable material and of suitable dimensions, such as pegs and/or nonslip products, making it possible to increase the adhesion between the mandrel and the fibers which will cover it.
The step of covering the first mandrel includes at least one phase of laying down at least one continuous fiber, which may or may not be impregnated with resin, along directions defined during the design of the countermold. The paths of the fibers are symmetrical with respect to at least one plane of symmetry of the first mandrel, with turnover regions in various sections of the mandrel so as to obtain at least one ply of fibers whose thicknesses are defined during the design of the countermold.
The step of covering the second mandrel includes at least one phase of laying down at least one continuous fiber, which may or may not be impregnated with resin, along directions defined during the design of the floating body. The paths of the fibers are symmetrical with respect to at least one plane of symmetry of the second mandrel, with turnover regions in various sections of the mandrel so as to obtain at least one ply of fibers whose thicknesses are defined during the design of the floating body.
The step of putting the materials of the floating body under pressure provides for an increase in the volume of the second mandrel and/or an infusion and/or an injection of resin and/or an expansion of resin, such as foaming resin, so as to obtain, on the one hand, a surface finish identical to that of the internal surface of the countermold and, on the other hand, a defined resin content.
By way of example, one embodiment of the subject of the invention is described below and illustrated schematically in the appended drawings, FIGS. 1 to 14, in which figures three orthogonal directions L, T and E are shown. The longitudinal direction, called L, corresponds to the axis of rotation of the winding apparatus and to the direction of normal movement of the floating body. The transverse direction, called T, is orthogonal to the direction L and lies in a horizontal plane passing through L. The height direction E is orthogonal to the directions L and T.